Emergency Medical Minute

Contributor: Taylor Lynch MD

• Supraventricular tachycardias (SVTs) arise above the bundle of His

• The term SVT includes AV nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT), atrial tachycardia, atrial fibrillation, atrial flutter, and multifocal atrial tachycardia

• AVNRT is the most common form of SVT

• Paroxysmal

• Spontaneous or provoked by exertion, coffee, alcohol, or thyroid disease

• More common in women (3:1 women:men ratio)

• HR 160-240

• Narrow complex with a normal QRS

• Unstable patients receive synchronized cardioversion at 0.5-1 J/kg

• Valsalva maneuver is attempted before pharmaceutical interventions

• Increases vagal tone at the AV node to slow conduction and prolongs its refractory period to normalize the conduction

• Traditionally, patients are asked to bear down, but this only works in 17% of patients

• REVERT trial assessed a modified valsalva that worked in 43% of patients

• Adenosine

• Slows conduction at the AV node by activating potassium channels and inhibiting calcium influx

• Extremely uncomfortable for most patients

• Not commonly used anymore

• Nondihydropyridine calcium-channel blockers are preferred

• A 2009 RCT investigated low-infusion CCBs compared with adenosine bolus

• The study found a conversion rate of 98% in the CCB group vs. adenosine group at 86.5%

• The main adverse effect of CCB is hypotension, which a slow infusion rate can mitigate

• Diltiazem dose is 0.25 mg/kg/2min and repeat at 0.35 mg/kg/15 minutes or slow infusion at 2.5 mg/min up to a conversion or 50 mg total

References

1. 1. Appelboam A, Reuben A, Mann C, et al. Postural modification to the standard Valsalva manoeuvre for emergency treatment of supraventricular tachycardias (REVERT): A randomised controlled trial. Lancet. 2015;386(10005):1747-1753. doi:10.1016/S0140-6736(15)61485-4

2. Belz MK, Stambler BS, Wood MA, Pherson C, Ellenbogen KA. Effects of enhanced parasympathetic tone on atrioventricular nodal conduction during atrioventricular nodal reentrant tachycardia. Am J Cardiol. 1997;80(7):878-882. doi:10.1016/s0002-9149(97)00539-0

3. Lim SH, Anantharaman V, Teo WS, Chan YH. Slow infusion of calcium channel blockers compared with intravenous adenosine in the emergency treatment of supraventricular tachycardia. Resuscitation. 2009;80(5):523-528. doi:10.1016/j.resuscitation.2009.01.017

4. Page RL, Joglar JA, Caldwell MA, et al. 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients With Supraventricular Tachycardia: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society [published correction appears in Circulation. 2016 Sep 13;134(11):e234-5. doi: 10.1161/CIR.0000000000000448]. Circulation. 2016;133(14):e506-e574. doi:10.1161/CIR.0000000000000311

Summarized & Edited by Jorge Chalit, OMS3

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